Evaluation of the 111In-(Sn)-citrate method to label antibodies for radioimmunotargeting studies.

Monoclonal antibody against carcinoembryonic antigen (CEA) was labeled by the 111In-(Sn)-citrate technique and its characteristics were determined from the point of radioimmunotargeting studies. Antibodies of high specific radioactivity could be labeled with a high labeling yield of greater than 90% without any further purification step, and without loss of immunoreactivity. In biodistribution studies using nude mice bearing CEA-producing tumors, an extremely high tumor-to-blood ratio (40 on day 6) was obtained since 111In in the blood cleared very rapidly, but nonspecific 111In localized in the liver and spleen should be seriously considered.